1. Field of the Invention
The present invention relates to firewall seals, and in particular, firewall seals utilized in aircraft engines.
2. Description of the Prior Art
The firewall requirements for aircraft engines are set out in regulatory requirements of the Federal Aviation Administration as set out in 14 CFR (1-1-86 Edition) Federal Aviation Administration, DOT regulation #25.1191 Firewalls:
(a) Each engine, auxiliary power unit, fuel-burning heater, other combustion equipment intended for operation in flight, and the combustion, turbine, and tailpipe sections of turbine engines, must be isolated from the rest of the airplane by firewalls, shrouds, or equivalent means. PA1 (b) Each firewall and shroud must be-
(1) Fireproof; PA2 (2) Constructed so that no hazardous quantity of air, fluid, or flame can pass from the compartment to other parts of the airplane; PA2 (3) Constructed so that each opening is sealed with close fitting fireproof grommets, bushings, or firewall fittings; and PA2 (4) Protected against corrosion.
At present, fuel line seal arrangements include four superimposed seal elements. Each seal element must have at least an entry slit to allow it to be installed on a fuel line, and the seal elements are placed on either side of the firewall to seal off the opening. Such a seal might be mounted with the slits in the seal elements aligned, thus providing a fire path through the seal.
Present seals are often made of asbestos and silicone rubber. These materials present no fire safety problems, but asbestos fibers are said to be a potential health hazard.